A solid polymer electrolyte fuel cell (Polymer Electrolyte Fuel Cell: hereinafter called “PEFC” as needed) has been developed as a fuel cell vehicle, a home cogeneration system, and the like.
As a catalyst used for the gas diffusion electrode of PEFC, a noble metal catalyst composed of a noble metal of platinum group elements such as platinum (Pt).
For example, as a typical conventional catalyst, there has been known “Pt on carbon catalyst” which is a powder of catalyst particles where Pt fine particles are supported on an electrically conductive carbon powder (hereinafter called “Pt/C catalyst” as needed).
For example, as the Pt/C catalyst, there has been known a Pt/C catalyst having a Pt support rate of 50 wt %, Trade Name: “NE-F50” available from N.E.CHEMCAT.
In the preparation costs of PEFC, a proportion of the noble metal catalyst such as Pt is large, and it is the problem to lower the PEFC cost and to spread PEFC.
To solve the problem, developments of technique for lowering the Pt in the catalyst layer of PEFC have been progressed. For example, in Non-Patent Document 1, there is described a summary of the developments until now.
Among these developments, in order to reduce the amount of platinum to be used, a powder (hereinafter called “core-shell catalyst” as needed) of a catalyst particle having a core-shell structure formed by a core part made of non-platinum element and a shell part made of Pt (hereinafter called “core-shell catalyst particle” as needed) has been studied, and there are many reports.
For example, in Patent Document 1, there is disclosed a particle composite material (corresponding to the core-shell catalyst particle) having a structure where palladium (Pd) or a Pd alloy (corresponding to the care part) is covered with an atomic thin layer of Pt atom (corresponding to shell part). Further in Example of this Patent Document 1, a core-shell catalyst particle having a structure where the core part is a Pd particle and the shell part is a layer made of Pt is described.
Further, for example, in Non-Patent Document 1, there is reported that a Pt on carbon catalyst (Pt/C) using a porous fine carbon power (carbon black) as a support has many fine pores in its inside, and Pt particles supported in the fine pores cannot be used effectively in the real reaction.
Furthermore in Non-Patent Document 1, there are disclosed two approaches for using the Pt in the above fine pores effectively, one approach where a high molecular electrolyte having a low molecular chain is designed and synthesized to disperse in the nano fine pores, and another approach to decrease the nano fine pores (method for using an electrically conductive ceramics support having no nano fine pore).
Incidentally, the present applicant submits, as publications where the above-mentioned publicly-known inventions are described, the following publications: